The subject invention relates to an emulsion coater having a unique extrusion head which permits pneumatic pressure to uniformly extrude emulsion under pressure. This emulsion coater is particularly useful for filling the mesh in silkscreens used by the printing industry. Unlike conventional mesh coating techniques which rely to a large extent on gravity as the driving force, the subject invention uses a pressure head that effectively eliminates the need to degrease a screen, providing both the economic and environmental benefits of not requiring a detergent.
Application of emulsion to a screen is labor intensive. Accordingly numerous automated machines have been developed to expedite this process. Unfortunately, current automated processes are basically variations on the manual process employed for decades. In the manual process, emulsion is exposed to a screen and dragged upward so as to disburse the emulsion across the surface of the screen. Unfortunately, a single coating will not fill all holes in the screen. Accordingly, the screen must be reversed and the process repeated again on the back side. This double application must again be repeated 2-4 more times depending on screen material and density.
Emulsions tend to be viscous. As such, they are difficult to dispense and typically require multiple passes with a squeegee to be forced through a printing screen. Moreover, it has been difficult to attain even distribution of emulsion through the screen. To achieve the above objectives, various devices have been utilized, none of which have proved entirely satisfactory.
U.S. Pat. No. 2,793,587, issued May 28, 1957 to Childers, brings out the problems associated with the use of a squeegee. One major disadvantage is the inability to obtain uniform pressure along the entire length of the squeegee. Further, mechanically supported squeegees have a tendency to sag in their midsections, or require special and complex mechanical support means.
The U.S. Pat. No. 4,550,681 issued Nov. 5, 1985 to Zimmer, et al., describes an applicator for uniformly distributing a flowable material over a receiving surface. This applicator uses a channel system having a branch channel structure extending from an entrance port through a multiplicity of exit ports. The channels become progressively more numerous and correspondingly narrower toward the exit ports. By having a large entry port leading to progressively smaller and smaller exit ports, to cause even distribution of fluid through the exit ports.
Like Zimmer, et al., the subject invention seeks to obviate pressure fluctuations which tend to form unsightly streaks and irregularities in the dispensed fluid. However, unlike Zimmer, et al., the subject invention utilizes equalization chambers and a final cover plate beyond the exit ports which result in smooth, even, pressurized delivery of the viscous emulsion to both coat and permeate a screen. The use of sufficient pressure to force emulsion through a screen is not taught or suggested by Zimmer, et al. Beyond the novel pressure head, the subject invention further provides a complete system for coating a screen with emulsion.